"""
Build database model definitions
"""

# -*- coding: utf-8 -*-
from __future__ import unicode_literals

from datetime import datetime

from django.contrib.auth.models import User
from django.utils.translation import ugettext as _
from django.core.exceptions import ValidationError

from django.urls import reverse
from django.db import models, transaction
from django.db.models import Sum
from django.core.validators import MinValueValidator

from InvenTree.status_codes import BuildStatus

from stock.models import StockItem
from part.models import Part, BomItem


class Build(models.Model):
    """ A Build object organises the creation of new parts from the component parts.

    Attributes:
        part: The part to be built (from component BOM items)
        title: Brief title describing the build (required)
        quantity: Number of units to be built
        take_from: Location to take stock from to make this build (if blank, can take from anywhere)
        status: Build status code
        batch: Batch code transferred to build parts (optional)
        creation_date: Date the build was created (auto)
        completion_date: Date the build was completed
        URL: External URL for extra information
        notes: Text notes
    """

    def __str__(self):
        return "Build {q} x {part}".format(q=self.quantity, part=str(self.part))

    def get_absolute_url(self):
        return reverse('build-detail', kwargs={'pk': self.id})

    title = models.CharField(
        blank=False,
        max_length=100,
        help_text='Brief description of the build')

    part = models.ForeignKey('part.Part', on_delete=models.CASCADE,
                             related_name='builds',
                             limit_choices_to={
                                 'is_template': False,
                                 'assembly': True,
                                 'active': True
                             },
                             help_text='Select part to build',
                             )
    
    take_from = models.ForeignKey('stock.StockLocation', on_delete=models.SET_NULL,
                                  related_name='sourcing_builds',
                                  null=True, blank=True,
                                  help_text='Select location to take stock from for this build (leave blank to take from any stock location)'
                                  )
    
    quantity = models.PositiveIntegerField(
        default=1,
        validators=[MinValueValidator(1)],
        help_text='Number of parts to build'
    )

    status = models.PositiveIntegerField(default=BuildStatus.PENDING,
                                         choices=BuildStatus.items(),
                                         validators=[MinValueValidator(0)],
                                         help_text='Build status')
    
    batch = models.CharField(max_length=100, blank=True, null=True,
                             help_text='Batch code for this build output')
    
    creation_date = models.DateField(auto_now=True, editable=False)
    
    completion_date = models.DateField(null=True, blank=True)

    completed_by = models.ForeignKey(User,
                                     on_delete=models.SET_NULL,
                                     blank=True, null=True,
                                     related_name='builds_completed'
                                     )
    
    URL = models.URLField(blank=True, help_text='Link to external URL')

    notes = models.TextField(blank=True, help_text='Extra build notes')
    """ Notes attached to each build output """

    @transaction.atomic
    def cancelBuild(self, user):
        """ Mark the Build as CANCELLED

        - Delete any pending BuildItem objects (but do not remove items from stock)
        - Set build status to CANCELLED
        - Save the Build object
        """

        for item in self.allocated_stock.all():
            item.delete()

        # Date of 'completion' is the date the build was cancelled
        self.completion_date = datetime.now().date()
        self.completed_by = user

        self.status = BuildStatus.CANCELLED
        self.save()

    def getAutoAllocations(self):
        """ Return a list of parts which will be allocated
        using the 'AutoAllocate' function.

        For each item in the BOM for the attached Part:

        - If there is a single StockItem, use that StockItem
        - Take as many parts as available (up to the quantity required for the BOM)
        - If there are multiple StockItems available, ignore (leave up to the user)

        Returns:
            A list object containing the StockItem objects to be allocated (and the quantities)
        """

        allocations = []

        for item in self.part.bom_items.all().prefetch_related('sub_part'):

            # How many parts required for this build?
            q_required = item.quantity * self.quantity

            stock = StockItem.objects.filter(part=item.sub_part)

            # Ensure that the available stock items are in the correct location
            if self.take_from is not None:
                # Filter for stock that is located downstream of the designated location
                stock = stock.filter(location__in=[loc for loc in self.take_from.getUniqueChildren()])

            # Only one StockItem to choose from? Default to that one!
            if len(stock) == 1:
                stock_item = stock[0]

                # Check that we have not already allocated this stock-item against this build
                build_items = BuildItem.objects.filter(build=self, stock_item=stock_item)

                if len(build_items) > 0:
                    continue

                # Are there any parts available?
                if stock_item.quantity > 0:

                    # Only take as many as are available
                    if stock_item.quantity < q_required:
                        q_required = stock_item.quantity

                    allocation = {
                        'stock_item': stock_item,
                        'quantity': q_required,
                    }

                    allocations.append(allocation)

        return allocations

    @transaction.atomic
    def unallocateStock(self):
        """ Deletes all stock allocations for this build. """

        BuildItem.objects.filter(build=self.id).delete()

    @transaction.atomic
    def autoAllocate(self):
        """ Run auto-allocation routine to allocate StockItems to this Build.

        Returns a list of dict objects with keys like:

            {
                'stock_item': item,
                'quantity': quantity,
            }

        See: getAutoAllocations()
        """

        allocations = self.getAutoAllocations()

        for item in allocations:
            # Create a new allocation
            build_item = BuildItem(
                build=self,
                stock_item=item['stock_item'],
                quantity=item['quantity'])

            build_item.save()

    @transaction.atomic
    def completeBuild(self, location, serial_numbers, user):
        """ Mark the Build as COMPLETE

        - Takes allocated items from stock
        - Delete pending BuildItem objects
        """

        for item in self.allocated_stock.all().prefetch_related('stock_item'):
            
            # Subtract stock from the item
            item.stock_item.take_stock(
                item.quantity,
                user,
                'Removed {n} items to build {m} x {part}'.format(
                    n=item.quantity,
                    m=self.quantity,
                    part=self.part.full_name
                )
            )

            # Delete the item
            item.delete()

        # Mark the date of completion
        self.completion_date = datetime.now().date()

        self.completed_by = user

        notes = 'Built {q} on {now}'.format(
            q=self.quantity,
            now=str(datetime.now().date())
        )

        if self.part.trackable:
            # Add new serial numbers
            for serial in serial_numbers:
                item = StockItem.objects.create(
                    part=self.part,
                    build=self,
                    location=location,
                    quantity=1,
                    serial=serial,
                    batch=str(self.batch) if self.batch else '',
                    notes=notes
                )

                item.save()

        else:
            # Add stock of the newly created item
            item = StockItem.objects.create(
                part=self.part,
                build=self,
                location=location,
                quantity=self.quantity,
                batch=str(self.batch) if self.batch else '',
                notes=notes
            )

            item.save()

        # Finally, mark the build as complete
        self.status = BuildStatus.COMPLETE
        self.save()

    def getRequiredQuantity(self, part):
        """ Calculate the quantity of <part> required to make this build.
        """

        try:
            item = BomItem.objects.get(part=self.part.id, sub_part=part.id)
            return item.get_required_quantity(self.quantity)
        except BomItem.DoesNotExist:
            return 0

    def getAllocatedQuantity(self, part):
        """ Calculate the total number of <part> currently allocated to this build
        """

        allocated = BuildItem.objects.filter(build=self.id, stock_item__part=part.id).aggregate(Sum('quantity'))

        q = allocated['quantity__sum']

        if q:
            return int(q)
        else:
            return 0

    def getUnallocatedQuantity(self, part):
        """ Calculate the quantity of <part> which still needs to be allocated to this build.

        Args:
            Part - the part to be tested

        Returns:
            The remaining allocated quantity
        """

        return max(self.getRequiredQuantity(part) - self.getAllocatedQuantity(part), 0)

    @property
    def required_parts(self):
        """ Returns a dict of parts required to build this part (BOM) """
        parts = []

        for item in self.part.bom_items.all().prefetch_related('sub_part'):
            part = {'part': item.sub_part,
                    'per_build': item.quantity,
                    'quantity': item.quantity * self.quantity,
                    'allocated': self.getAllocatedQuantity(item.sub_part)
                    }

            parts.append(part)

        return parts

    @property
    def can_build(self):
        """ Return true if there are enough parts to supply build """

        for item in self.required_parts:
            if item['part'].total_stock < item['quantity']:
                return False

        return True

    @property
    def is_active(self):
        """ Is this build active? An active build is either:

        - PENDING
        - HOLDING
        """

        return self.status in BuildStatus.ACTIVE_CODES

    @property
    def is_complete(self):
        """ Returns True if the build status is COMPLETE """
        return self.status == BuildStatus.COMPLETE


class BuildItem(models.Model):
    """ A BuildItem links multiple StockItem objects to a Build.
    These are used to allocate part stock to a build.
    Once the Build is completed, the parts are removed from stock and the
    BuildItemAllocation objects are removed.

    Attributes:
        build: Link to a Build object
        stock_item: Link to a StockItem object
        quantity: Number of units allocated
    """

    def get_absolute_url(self):
        # TODO - Fix!
        return '/build/item/{pk}/'.format(pk=self.id)
        # return reverse('build-detail', kwargs={'pk': self.id})

    class Meta:
        unique_together = [
            ('build', 'stock_item'),
        ]

    def clean(self):
        """ Check validity of the BuildItem model.
        The following checks are performed:

        - StockItem.part must be in the BOM of the Part object referenced by Build
        - Allocation quantity cannot exceed available quantity
        """
        
        super(BuildItem, self).clean()

        errors = {}

        try:
            if self.stock_item.part not in self.build.part.required_parts():
                errors['stock_item'] = [_("Selected stock item not found in BOM for part '{p}'".format(p=self.build.part.full_name))]
            
            if self.quantity > self.stock_item.quantity:
                errors['quantity'] = [_("Allocated quantity ({n}) must not exceed available quantity ({q})".format(
                    n=self.quantity,
                    q=self.stock_item.quantity
                ))]

        except StockItem.DoesNotExist:
            pass

        except Part.DoesNotExist:
            pass

        if len(errors) > 0:
            raise ValidationError(errors)

    build = models.ForeignKey(
        Build,
        on_delete=models.CASCADE,
        related_name='allocated_stock',
        help_text='Build to allocate parts'
    )

    stock_item = models.ForeignKey(
        'stock.StockItem',
        on_delete=models.CASCADE,
        related_name='allocations',
        help_text='Stock Item to allocate to build',
    )

    quantity = models.PositiveIntegerField(
        default=1,
        validators=[MinValueValidator(1)],
        help_text='Stock quantity to allocate to build'
    )